Abstract:
The Tennessee Valley Authority’ s Boone Dam was constructed in the 1950’ s using
construction techniques for embankment dams built on karst foundations that were
common to the contemporary state of the practice. These techniques included excavation
of a cutoff trench to rock where the exposed limestone pinnacles were cleaned of loose,
soft, or otherwise permeable materials and backfilled with compacted clay and construction
of a grout curtain along the cutoff trench alignment. After a sinkhole opened near the
downstream toe of the embankment and turbid water was observed exiting from the right
bank of the tailrace in 2014, TVA embarked on a comprehensive remediation project to
mitigate the active internal erosion failure modes including two production drilling and
grouting programs, construction of rockfill berms on the upstream and downstream faces
of the embankment, and construction of a concrete secant pile wall. Drilling and grouting
was used in this comprehensive remediation as an interim risk reduction measure in zones
of well developed karst, as a primary treatment in groutable rock, as an exhaustive
subsurface exploration program used as the design basis for the concrete cutoff wall, and
as a detailed verification program to confirm the constructed cutoff wall would meet the
design intent of permanently mitigating internal erosion related failure modes. This paper
discusses the drilling and grouting methods employed across the phases of the project and
how the data from individual grouting programs was incorporated into subsurface models,
the design of subsequent phases of construction, and final acceptance of the remediation.